The present invention relates to a method of manufacturing metallic or electrically-conductive structures on non-conductors or non-conductive surfaces.
Electrically conductive structures or conductive paths are normally produced on substrates made of ceramics, plastics, glass and various non-conductive compounds. Conductive paths should be manufactured with high precision to meet requirements of numerous applications of such structures in contemporary electronics.
The production of such conductive paths is usually obtained by a wet chemical process which means that a non-conductive outer surface which is provided with a conductor-building mask is immersed into wetty solutions of washing and conditioning agents and then is placed into noble metal-containing solutions, mostly palladium-containing solutions, and is there "contaminated" with noble metal ions. These "contaminated" particles are then reduced in solutions containing a reduction agent to metallic atoms. Finally a suitable metallizing takes place in a chemically-reductive copper or nickel bath operating without external current. The object being treated is thoroughly rinsed in clean water between the operations.
The above described method has, however some disadvantages which reside in that many working and rinsing steps are required. Also, there is the danger that the treatment solutions would be contaminated by residuals adherent to the substrate treated by previous solutions, this would result in a non-satisfactory metallizing. Treatment solutions are partially agressive and can cause damage or distortion of a covering lacquer or foil; therefore unclean metallic structures result, particularly in case of fine conductive paths which can lead to a partial or complete failure of produced printed circuit boards during further application.
Plasma (glow discharge) has been utilized before for various purposes. For example, hydroxides of aluminum oxide ceramics have been produced in plasma as well as hydroxides of silicon, siliconoxides and siliconnitrides.
Another field in which glow discharge or plasma arc has been utilized is the method of manufacturing thin polymer layers or coatings on solid-state bodies made of inorganic monomers. In the same manner are produced hard resistant polymer films with high isolating properties, for example of acetylene, styrol, benzene, metane, etc. in the presence of carrier gases such as helium and argon. If additional metallo-organic compounds, for example tetramethyl tin, are found in the gas mixture polymeric organometallic films are obtained. Pure metal-oxides which are very important in the field of sensor and semiconductor electronics can be made in the same manner of metalloorganic compositions with the carrier gas or without the latter under the effect of glow discharge.
Also, the decomposition of the nickeltetracarbonate to metallic nickel and the decomposition of the molybdenum hexacarbonyl to molybdcnum-carbon films have been disclosed; the disclosures, however, give no hint that certain metallic structures can be produced on non-conductive surfaces. It should be also considered that metalcarbonyls are highly poisonous cancer-causing substances which have found no technical applications.
Also known is the thermal decomposition of metalloorganic compounds in vacuum whereby metallic coatings can be deposited on a substrate. However, in this known method, the substrate must be heated up to at least 200.degree. C., in practice to 300.degree.-400.degree. C.